What? Where? If you can tell when someone’s sneaking up on you, your ears might have a good sound localization ability, meaning they're great at judging sound direction.

Problem

How well do people sense the direction of a sound?

Materials

Grassy field

Lots of string

Protractor

Nails or wire stakes

Plastic freezer bag

Flour

Blindfold

Jingle bell

Tape measure

2 or more friends

Procedure

Can your friends determine the direction of a sound? How well can they pinpoint the direction that a sound is coming from? Create a hypothesis, your best guess about what is going to happen. What directions are the easiest to identify? Which ones are the hardest?

First, you’ll create a semicircle so that you can make sounds in different places. To build your circle, put a nail in the ground and tie one end of a spool of string to the nail. Measure out 30 meters of string and pull the string taut. Put another nail in the ground and tie the other end of your string to the nail. This length of string will act as the diameter of your semicircle.

Walk along the string until you get to the middle. Put a nail at that point, and tie more string to that nail. The new string should be 15 meters long. Walk to one end of the diameter, holding the new string. Start walking in a curved path, holding the string taut. As you walk, you or a friend can hold a plastic freezer bag of flour with the corner clipped off and use it to mark a semicircle on the grass.

Now it’s time to make some noise! Ask one of your friends to stand at the midpoint, the place where you put the second nail. Put a blindfold on your friend so that he will have to use only his ears to pinpoint the direction of the sound.

Measure out another 15-meter length of string for yourself, and give your 2nd friend his own 15-meter length of string and a jingle bell. Tie the ends of these strings to the nail close to where the blindfolded subject is standing. You and your friend should stand at the edge of the circle, holding your strings to either side of your blindfolded friend.

Have your friend with the jingle bell quietly move along the edge of the circle, stop, and jingle the bell. Ask your blindfolded test subject to point to the place where he heard the bell. Walk around the edge of the circle to move your string so that it lines up with the place your blindfolded friend is pointing. Ask your blindfolded friend to take his blindfold off and measure the angle that each string makes with the semicircle’s diameter. Place the results into a table:

Test Subject

True Angle

Guessed Angle

Difference

Subject One

Do five trials for each blindfolded test subject, then ask your friends to switch jobs.

How accurate were your friends’ guesses? Was one person more accurate than the others, or were they all similar? What directions were most difficult for your friends to guess?